Added syn_useioff attribute support for Oxide toolchain and for the DDRTristate in Crosslink NX

Signed-off-by: Maciej Kurc <mkurc@antmicro.com>

litex/build/lattice/common.py

@@ -309,6 +309,7 @@ class LatticeNXDDRTristateImpl(Module):
         self.specials += SDROutput(oe1|oe2, _oe, clk)
         self.specials += DDRInput(_i, o1, o2, clk)
         self.specials += Tristate(io, _o, _oe, _i)
+        _oe.attr.add("syn_useioff")
 
 class LatticeNXDDRTristate:
     @staticmethod

litex/build/lattice/oxide.py

@@ -108,6 +108,7 @@ def _run_script(script):
 class LatticeOxideToolchain:
     attr_translate = {
         "keep": ("keep", "true"),
+        "syn_useioff": ("syn_useioff", 1),
     }
 
     special_overrides = common.lattice_NX_special_overrides_for_oxide